The present invention relates to a developing apparatus for applying a developer onto a latent image formed on an image carrier to develop the latent image.
Developers used in developing apparatuses of this type include one-component developers and two-component developers. A two-component developer consists of a toner contributing to development and a carrier for properly charging this toner. However, in such a two-component developer, a mixing ratio of the toner to the carrier must be kept constant. In other words, the toner concentration must be kept constant. However, it is difficult to maintain a constant toner concentration. On the other hand, a one-component developer has an advantage in that the concentration can be easily controlled since only the toner for contributing to development is contained in the developer.
One-component developers are classified into magnetic and nonmagnetic developers. Magnetic developers contain magnetic materials in the nonmagnetic developer particles. When such a magnetic developer is used in a conventional apparatus, a magnet is arranged on the inside of a developer carrier for carrying the developer into the developing position and generating a magnetic field for supporting the developer. The following problems occur when the magnetic developer is used.
(1) The developer carrier becomes complicated, expensive and large since the magnet must be supported by the developer carrier.
(2) A magnetic developer containing magnetic particles is more expensive than a nonmagnetic developer.
(3) Since a magnetic developer contains magnetic particles which do not contribute to development, color reproducibility is not so good. As a result, it is difficult to perform color development using a magnetic developer.
In the case of using either developer, when developer is applied to the developing position opposite to the image carrier, excessive developer which is not subjected to developing can be applied because there is no regulation to the developer. For this reason, when the developing image is transferred to a sheet, the excessive developer is also transferred to the sheet, thereby contaminating the transferred image. In addition to this disadvantage, the excessive developer leaks and drips from the developing apparatus.